Actually, I think I won't be able to explain well for my English, besides I understand it as "one expression / set phrases" without thinking about the particles, so please wait for the better answers. The basic translation of も is ltoo / also" in English, and we use it to enumerate more than two things. About the first sentence, if we separate it in two sentences, it' この町にはデパートがありません。スーパーもありません。Two in one sentence, since BOTH aren't in this town, in Japanese grammar, we use the structure 〜もなければ〜もない. It's "set About the second sentence, in two sentences, it's 山田さんは歌を歌う。 and ギターも弾く。Then two in one, 歌も歌えばギターも弾く。He can do BOTH so, we use the structure 〜もすれば〜もする. I hope this was helpful even though it's only a little.

I think we need more details or if you have English translation, please write it.